Authorities said Thursday the volcanic eruption does not pose any danger to Tonga islanders at this stage, and there have been no reports of fish or other animals being affected.
Spectacular columns are spewing out of the sea about 6 miles (10 kilometers) from Tonga's main island of Tongatapu—an area where up to 36 undersea volcanoes are clustered, geologists said (Tonga map).
Trade winds continued to blow volcanic gas and steam away from the island Thursday.
Taniela Faletau, deputy commander of the Tonga police force, said coastal villages close to the roiling ocean site were not yet at risk from the volcanic eruption. No warnings have been issued.
Scientists and government officials sailed Thursday to inspect the volcano, and police are waiting for the team's observations before taking any action.
Coastal residents said the volcanic steam and ash column first appeared on Monday morning, after a series of sharp earthquakes were felt in Tonga's capital, Nuku'alofa.
"This is not unusual for this area and we expect this to happen here at any time," said Keleti Mafi, Tonga's geological service head.
The underwater volcanic eruption was taking place near the low-lying twin volcanic islands of Hunga Tonga and Hunga Ha'apai, within sight of Nuku'alofa.
Large amounts of pumice thrown up by the volcanic eruption would likely clog beaches on the southern coast of the nearby Fiji Islands within a short time, Mafi said.
Tonga, a 170-island archipelago about halfway between Australia and Tahiti, is part of the Pacific Ring of Fire—an arc of earthquake and volcanic zones stretching from Chile in South America through Alaska and down through Vanuatu to Tonga.
(Related: "Giant Undersea Volcano Found Off Iceland.")